1. Field of the Invention
This invention relates to improved carbonless papers for electrophotographic copiers, copier/duplicators, and laser printers. Carbonless papers manufactured as grain-short paper and wherein the grain direction is parallel to the direction of feed when printed upon in electrophotographic copiers, copier/duplicators, and laser printers results in reduced paper jams, reduced paper curl, and allows the use of lower basis weight papers and the use of non-xerographic grade papers than that normally used in electrophotography.
2. Background of the Art
Carbonless impact marking papers for the transfer of images, (i.e., carbonless copy papers) are papers which are capable of producing an image upon application of pressure.
Products employing this chemistry generally comprise at least two reactants, one reactant known as a color-former and the other reactant known as a developer. Means for preventing the reaction of the two until intended (i.e., until activating pressure is applied) are also provided. This is typically accomplished by encapsulation of one of the reactants. Preferably, a fill solution of the color-forming compound(s) in a hydrophobic solvent is encapsulated or contained in microcapsules. The microcapsules serve the purpose of isolating the reactants from one another and preventing reaction. Once activating pressure is applied to the uncoated surface of a top sheet, such as from a stylus (e.g., a pencil or pen) or business-machine key (e.g., a typewriter or impact printer), the two reactants come into contact under sufficient pressure so that the capsules rupture (i.e., those capsules corresponding to the pattern of applied pressure) and the solution of encapsulated color-former is released and a reaction between the previously separated reactants occurs. Since the color-former and the developer form a deeply colored image when reacted, an image forms on the lower sheet. In general, the resulting reaction will, of course, form a colored image corresponding to the path traveled by the stylus or the pattern of pressure provided by the stylus or key. The term "activating pressure" includes, but is not limited to, pressure applied by hand with a stylus or pressure applied by a business machine key and the terms "encapsulation" and "encapsulated compounds" refer to microcapsules enclosing a fill material.
The chemistry used in carbonless papers is of two general types. In one type of carbonless paper, the image results from the reaction between an encapsulated leuco dye color-former and an acid, a phenolic, or acidic clay developer. In another type of carbonless paper, the image results from the formation of a colored coordination compound by the reaction between an encapsulated ligand color-former and a transition metal developer.
A preferred construction contains an encapsulated color-former dissolved in appropriate hydrophobic solvent(s) within microcapsules and coated with a suitable binder onto a backside of the donor sheet, sometimes referred to as a "coated back" (CB) sheet. A developer, also optionally in a suitable binder such as a starch or latex, is coated onto the front side of the receptor sheet sometimes referred to as a "coated front" (CF) sheet. The term "suitable binder" refers to a material, such as starch or latex, that allows for dispersion of the reactants in a coating on a substrate. Each CB coating contains capsules which, when ruptured, release reagents to produce a color-changing reaction at the adjacent CF coating. The preparation of such capsules and of such carbonless sheets is disclosed by in U.S. Pat. Nos. 3,516,846 and 3,516,941.
A wide variety of processes exist by which microcapsules can be manufactured and a wide variety of capsule materials can be used in making the capsule shells, including gelatin and synthetic polymeric materials. A popular material for shell formation is the product of the polymerization reaction between urea and formaldehyde (UF capsules); between melamine and formaldehyde (MF capsules); or the polycondensation products of monomeric or low molecular weight polymers of dimethylolurea or methylolated urea with aldehydes.
As stated previously, the two sheets are positioned such that the backside of the donor sheet faces the developer coating on the front side of the receptor sheet. In many applications the uncoated surface of the donor (CB) and receptor (CF) sheets contain preprinted information of some type and the activating pressure is generated by means of a pen or other writing instrument used in filling out the form. Thus, the image appearing on the receptor sheet is a copy of the image applied to the front side of the top sheet.
Constructions containing a first substrate surface, on which is coated the encapsulated color-former, and a second substrate surface, on which is coated a developer, are often prepared. The coated first substrate surface is positioned within the construction in contact with the coated second substrate surface. Such a construction is known as a "set" or a "form-set" construction.
Substrates, with one surface, on which is coated the encapsulated color-former, and a second, opposite surface, on which is coated a developer, can be placed between the CF and CB sheets in a construction involving a plurality of substrates. Such sheets are generally referred to herein as "CFB" sheets (i.e., coated front and back sheets). Of course, each side including color-former thereon should be placed in juxtaposition with a sheet having developer thereon. CFB sheets are also typically used in form-sets. In some applications, multiple CFB sheets have been used in form-sets. These contain several intermediate sheets, each having a developer coating on one side and a coating with capsules of color-former on the opposite side. Thus, the sheets in the form-set are sequenced in the order (from top to bottom) CB, CFB(s), and CF. This insures that in each form-set a color former and a color developer will be brought into contact when the microcapsules containing the color-forming material are ruptured by pressure.
An alternative to the use of CB, CF, and CFB sheets is the self-contained (SC), or autogenous, carbonless paper in which both the color-former and developer are applied to the same side of the sheet and/or are incorporated into the fiber lattice of the paper sheet.
Carbonless paper is often used in pre-printed form-sets for preparing multiple copies of receipts, bills, and other business forms and form-sets are prepared by collating from 2 to 8 sheets of carbonless paper. Typically, preprinted forms are compiled into a set or packet such that marking the top form will provide the required number of duplicates. If the number of duplicates is greater than about 3, (i.e., a 4-part form set) the carbonless paper is often manufactured on low basis weight paper so that the pressure exerted on the top sheet will rupture the capsules on the fourth and subsequent sheets in the set. This ability to form a good, dark legible image on a bottom sheet of a form-set from pressure applied on a top sheet, is known as "manifolding."
Form-sets are typically made by applying an adhesive to the edge of a stack of sequenced (i.e., collated) carbonless paper. Each of the coated sheets in a form-set is somewhat porous and permits the adhesive to penetrate into the pores of the paper, such penetration being necessary to attain satisfactory adhesion of sheets within the form-set. Adhesives useful for edge-padding carbonless papers are described, for example, in U.S. Pat. No. 5,079,068.
The adhesively bound papers are then "fanned-out" to be separated into individual form-sets. To promote separation, carbonless copy paper form-sets often have a release coating (for example, a fluorocarbon or silicone coating) applied to at least one of the outer faces of each form-set. These coatings are often referred to as "pad coats." Pad coats function as an abhesive (i.e., a non-adhesive) to provide low adhesion properties to the outer faces of a form-set; as a release agent for the edge-padding adhesive; and to promote "fan-out properties" in edge-padding to allow the adhesively edge-padded stack to "fan-out" or "fan-apart" and separate into individual form-sets upon fanning. Individual form-sets are prepared by stacking the collated carbonless paper, trimming, edge-padding with an edge-padding adhesive, and fanning-out. "Fan-out" is a method of separating a stack or pad of multiple form-sets into individual form-sets.
Often carbonless paper is prepared and packaged in precollated unpadded form-sets. In one version, referred to as a "straight sequence form-set," the sheets are arranged in the order in which they will appear in the finished form. In these form-sets, the coated back sheet (CB) is first in the form-set, the coated front sheet (CF) is last, and the required number of CFB sheets are in between. Alternatively, the paper may be prepared and packaged in precollated form-sets referred to as "reverse sequence form-sets," wherein sheets of various colors and surfaces are arranged opposite to their normal functional order. The coated front sheet (CF) is first in the form-set, the coated back sheet (CB) is last, and the required number of CFB sheets are in between. When sheets are arranged in this manner and are printed in a printer or copier which automatically reverses their sequence, they will end up in the delivery tray in the proper order for subsequent padding and data entry. The type of sequenced form-set used for a particular printing operation is a function of the printing machinery.
Carbonless paper is widely used in the forms industry and carbonless paper forms have been printed in the past by conventional printing techniques such as offset printing, lithography, etc. With the advent of high speed electrophotographic copiers, copier/duplicators, and laser printers having dependable, high capacity collating systems and enhanced copy quality, there has been a movement to replace offset printing equipment located in print shops and large "quick-print" installations with electrophotographic copiers.
Attempts to run conventional carbonless papers through electrophotographic copiers have proved difficult and have resulted in capsule rupture with contamination and damage to copier components, poor machine performance, degraded quality of photocopies, carbonless paper smudging, sheet misfeeds, multi-sheet feeds, paper jams, folded corners, poor manifolding, and curled sheets. For the successful use of carbonless papers in electrophotographic copiers, compatibility of the carbonless paper with the machine is critical. For example, the base sheets upon which carbonless paper coatings are applied to form carbonless papers conventionally imaged via offset printing do not have sufficient stiffness or sufficient sensitivity to machine conditions for curl and moisture control to be handled in copier processors and sorters. Undesirable curl can result in a number of problems within a photocopier and can affect paper feed, transport, image registration, toner fusing and sorter stacking.
Paper jams in high speed copiers, copier/duplicators, and laser printers are particularly troublesome when carbonless papers are used. Jamming destroys the correct sequence of sheets and results in form-sets with missing sheets. The photocopier needs to be opened, the jammed sheets removed, and an additional number of sheets needs to be removed so that the integrity of the stack of form-sets is maintained. This is time consuming and difficult and results in down-time and lost production.
One solution to the problems encountered when carbonless papers are printed upon in high speed photocopiers disclosed in U.S. Pat. No. 4,906,605. That patent discloses the preparation of carbonless papers using high basis weight paper coupled with smaller capsule size and tighter capsule size distribution, along with the elimination of stilt materials containing solvents, allows the successful use of these carbonless papers within copiers such as the Xerox 9000 series copiers and printers.
Another solution to problems encountered when carbonless papers are used in high speed copiers is taught in U.S. Pat. No. 5,084,433. That patent discloses the use of improved solvents compatible with electrophotographic copiers.
A further improvement in preventing capsule rupture and copier damage as well as improving runnability of carbonless paper in photocopiers, copier/duplicators, and laser printers is taught in European Laid Open Patent Application EP 0,569,285. Misfeeding is reduced by preparing carbonless copy paper sheets in which the coefficients of friction of the various faces of the paper are kept within 0.1 units of each other.
Another approach to improved carbonless papers for use in electrophotographic copiers is taught in Copending U.S. patent application Ser. No. 08/047,848, filed Apr. 15, 1993, wherein the use of a pea starch as a stilt material was found to markedly reduce capsule rupture in the printing of carbonless paper in electrophotographic copiers.
Thus, an ability to run carbonless papers through electrophotographic copiers, copier/duplicators, and laser printers has been achieved, but has required the use of heavy basis weight paper (generally about 20 lbs.) or specially prepared xerographic paper. As mentioned earlier, high basis weight papers are disadvantageous when 4-part or greater carbonless paper form-sets are required. Thus, runnability has been achieved at the expense of manifolding. It would be desirable to have a carbonless paper which would provide carbonless sheets which lay flat, can run through photocopiers, are capable of double-sided copying, and exhibit good manifolding.